This is something I frequently noticed in budgies behaviour.
When one budgie is ill, he puffs up his feathers and sits on the perch with his eyes closed.
The other budgies around him know what is going on, they can tell that their buddy is not feeling well.
Budgies seem to know what might happen when another budgie starts closing his eyes... and they don't want the budgie to fall asleep forever. Because of that, they poke the sick budgie whenever they catch him dozing off.
It's a friendly but decisive poke with the beak, acting as a safety measure to keep the sick budgie awake... and alive!